From: Rich Felker <dalias@aerifal.cx>
Date: Wed, 28 Sep 2011 23:45:37 +0000 (-0400)
Subject: fix excessive/insufficient wakes in __vm_unlock
X-Git-Url: http://nsz.repo.hu/git/?p=musl;a=commitdiff_plain;h=de543b05c87d79a9313991810e9ee8ecdaad8f19

fix excessive/insufficient wakes in __vm_unlock

there is no need to send a wake when the lock count does not hit zero,
but when it does, all waiters must be woken (since all with the same
sign are eligible to obtain the lock).
---

diff --git a/src/thread/pthread_barrier_wait.c b/src/thread/pthread_barrier_wait.c
index 71f7b5fe..6052925a 100644
--- a/src/thread/pthread_barrier_wait.c
+++ b/src/thread/pthread_barrier_wait.c
@@ -13,9 +13,9 @@ void __vm_lock(int inc)
 
 void __vm_unlock(void)
 {
-	if (vmlock[0]>0) a_dec(vmlock);
-	else a_inc(vmlock);
-	if (vmlock[1]) __wake(vmlock, 1, 1);
+	int inc = vmlock[0]>0 ? -1 : 1;
+	if (a_fetch_add(vmlock, inc)==-inc && vmlock[1])
+		__wake(vmlock, -1, 1);
 }
 
 static int pshared_barrier_wait(pthread_barrier_t *b)